A hacker convention located in Las Vegas every summer where people go to:
1: Learn about the latest computer vulnerabilities, exploits, mods, and hacks.
2: Participate in (generally) computer related contests such as Capture the Flag, Wardriving, Wi-Fi Shootout, Scavenger Hunt, and Spot the Fed.
2: Get trashed and hang out with fellow geeks.

"Defcon, where you walk in a n00b, and walk out a 1337 HaXX0R!!1!eleven."
"Dude, we actually got some depleted uranium for the scavenger hunt for 80 points!"
"During PoolCon, I got soooo shitfaced and made out with one of the haxxxor girls.... or at least I think it was one of them."

Stands for "defecation condition" - a play off of the government acronym for "defense condition". Refers to the varying, and usually scaling, levels of severity relating to an impending bowel movement. The direction of the sliding scale varies from user to user, but typical usage labels Defcon 1 as the least urgent, and Defcon 5 as an imminent expulsion (the opposite of the defense department's usage).

Dude, I was at Defcon 5 and nearly shit my pants. Luckily we drove by a Carl's Jr. and I was able to drop a load.